The present invention relates to a device for embossing and laminating continuous plies for forming a web material.
More particularly, the present invention relates to an embossing and laminating device of the type comprising a pair of embossing cylinders, each co-operating with a respective pressure roll, with a glue applicator for applying an adhesive onto at least one of the embossed plies, and with laminating means which cause joining together of two plies separately embossed between each embossing cylinder and the respective pressure roll.
In the paper converting industry, for the production of toilet paper, all-purpose drying paper, paper napkins, tissue paper in general and similar products, embossing is frequently used in order to modify the characteristics of softness and absorbency of the paper.
Different embossing and joining systems exist for the production of embossed web materials obtained by joining together several plies. In particular, there are systems in which the two or more plies of continuous material are separately embossed and then joined together. These systems can be divided up basically into tip-to-tip joining systems and nested joining systems, so-called random nesting or xe2x80x9cDERLxe2x80x9d systems or the like.
In the first case (see EP-B-0,370,972), two plies are each embossed between an embossing cylinder, provided with projections or tips arranged in a repetitive pattern, and a pressure roll, normally lined with resilient material, such as rubber or the like. Subsequently the two plies are joined together by means of laminating between the two facing embossing cylinders which are phase-synchronized with one another so that, in the laminating nip between the two cylinders, the tips of one cylinder are located opposite the tips of the other one, the distance between the cylinders being such as to cause laminating of the plies between the facing tips. Usually, before laminating, an adhesive is applied onto one of the two plies, in the relief zones produced by embossing.
Nested-type embossing and joining together, on the other hand, involves the plies which are separately embossed in a similar manner to that described above being joined together so that the projections of one ply are arranged in between the projections of the other one. In such cases the two embossing cylinders are not pressed against one another in the nip between them and the two plies are joined together by means of laminating between one of the two embossing cylinders and a joining roller. This technique is described in GB-B-1,225,440 and in U.S. Pat. No. 3,694,300.
Italian patent No. 1,213,842 (Application No. 9519A/87) describes an embossing unit of the tip-to-tip type which has been modified so as to be able to produce nested embossing of the random type (xe2x80x9cDERLxe2x80x9d). This is obtained by introducing a deviating element which modifies the path of one of the two plies between the embossing zone and the laminating zone.
Italian Utility Model Application No. 21,325B/89 describes a device which allows embossing both of the nested type and embossing of the tip-to-tip type to be performed by modifying as required the arrangement of the components of the device. Basically, in order to change from one type of processing to the other type, it is necessary to modify entirely the arrangement of the embossing cylinders. In fact, according to this known technique, it is suggested basically to convert on each occasion a proper tip-to-tip embossing unit into a proper nested embossing unit. This involves very long operation times in order to pass from one type of embossing system to the other. Moreover, in this device, in order to be able to arrange the laminating roll in a position such that it is able to cooperate with one of the embossing cylinders, it hasbeen necessary to arrange the axes of the two embossing cylinders and the two pressure rolls on a single common horizontal plane. This involves considerable drawbacks due to the deformations of the embossing cylinders, caused by the high pressures necessary for embossing, with consequent non-uniform embossing and laminating of the plies between the center and the edges.
The object of the present invention is to provide an embossing/laminating device which is able to operate in tip-to-tip or nested mode and which allows easy conversion from one type of embossing to the other, reducing to a minimum the operations of adjustment and regulation of the device.
Yet another object of the present invention consists in providing a configuration which allows the existing embossing/laminating units, of the tip-to-tip-type, to be converted in a rapid and economic manner into dual-purpose embossing/laminating units suitable for producing embossed material (comprising several glued plies) using the nested technique and the tip-to-tip technique, alternately.
A further object of one improved embodiment of the present invention is the provision of an embossing unit in which the embossing cylinders and the pressure rolls are arranged so as to reduce the irregularities in the laminated product due to the flexural deformations of the embossing cylinders.
These and further objects and advantages, which will become clear to those skilled in the art from reading of the text which follows, are obtained in an embossing and laminating device of the type comprising: a first and a second embossing cylinder, provided with associated tips or projections, said two embossing cylinders being arranged with parallel axes and arranged adjacent to one another so as to form a nip between them; a pair of pressure rolls, each of which co-operates with one of the embossing cylinders; an adhesive applicator associated with the first embossing cylinder; and a laminating roll arranged downstream of the nip between the embossing cylinders and cooperating with the first embossing cylinder. Basically, according to the invention it is envisaged that the planes containing the axis of each embossing cylinder and the axis of the corresponding pressure roll are both inclined with respect to the plane containing the axes of the embossing cylinders at an angle different from 0xc2x0 and 90xc2x0 and that the angle formed by the plane containing the axis of the first embossing cylinder and the respective pressure roll with the plane containing the axes of the two embossing cylinders and directed towards said nip is greater than 90xc2x0. Moreover, it is envisaged that said two embossing cylinders should have the same peripheral speeds and that they may be phase-synchronized with each other so as to bring the tips of one embossing cylinder opposite the tips of the other embossing cylinder, or alternatively cause the tips of one embossing cylinder to engage in between the tips of the other embossing cylinder, without necessarily modifying the interaxial distance between the cylinders.
In this case, a greater space for arranging the marrying or laminating roll is created around the first embossing cylinder. This allows one to pass from the tip-to-tip configuration to the nested configuration without moving the embossing cylinders away from one another. The existing tip-to-tip embossing units may be easily modified so as to vary the mutual position of the axes of the pressure rolls and the embossing cylinders and introduce into the space thus formed a laminating roll, this making the unit suitable for producing also web material embossed and joined using the nested technique.
The embossing cylinders may have symmetrical tips arrangements or (in particular when the device is operating in the nested configuration) non-symmetrical arrangements. The embossing cylinders may also be replaced when the device changes over from the tip-to-tip configuration to the nested configuration, or vice versa. The phase-displacement between the tips of an embossing cylinder and the tips of the other cylinder may be obtained with an angular movement or also with a mutual axial movement of the cylinders. In other words, while keeping one of the cylinders at a standstill, the other cylinder may be rotated about its axis, or translated parallel to its axis, by an amount such as to cause its tips to engage in between the tips of the other cylinder.
According to an advantageous embodiment of the present invention, it is also envisaged that the two planes containing the axes of the embossing cylinders and the respective pressure rolls are inclined in directions such as to cause deformations which have components coinciding in the plane containing the axes of the two embossing cylinders. This is obtained by arranging the pressure roll associated with the first embossing cylinder in an angular position which is further away from the nip and the pressure roll associated with the second embossing cylinder closer to the nip. The stresses exerted by the two pressure rolls thus cause, in the plane containing the axes of the two embossing cylinders, deformations in the same direction, which do not affect the conditions of contact between the tips in the laminating nip also when the embossing unit operates using the tip-to-tip technique. A more uniform and regular product is thus obtained.
Further embodiments of the present invention are indicated in the accompanying dependent claims.